Process of producing ferrosilicon.



H. C. HARRISON. PROCESS OF'PRODUCING FERROSILICON.

APPLICATION FILED JUNE I2, I912.

1 1 7 l 7 1 9 Patented Feb. 15, 1916.

WITNESSES )NVENTOR UNITED STATES OFFICE.

HERBERT CHAMPION HARRISON, OF NIAGARA FALLS, NEW YORK, ASSIGNOR T0 ELECTRO METALLURGICAL COMPANY, OF NIAGARA FALLS, NEW YORK, A COR- PORATION OF WEST VIRGINIA.

PROCESS OF PRODUCING FERROSILICON.

Specification of Letters Patent.

Patented Feb. 15, 1916.

Application filed June 12, 1912. Serial No. 703,261.

To all whom it may concern Be it known that I, HERBERT C. HARRI- SON, a subject of the King of Great Britain, residing at Niagara Falls, in the county of Niagara and State of New York, have invented certain new and useful Improvements in Processes of Producing Ferrosilicon, of which the following is a specification.

Many difficulties are encountered in the commercial operation of large ferrosilicon furnaces, on account of the electrical, chemical, thermal and mechanical conditions involved. Not only must the charge consist of materials having the purity requisite for the desired product, but it must have the proper physical characteristics: it must feed freely, and must be of low electrical conductivity, to enable the electrodes to extend downward to a smelting zone near the bottom of the furnace, without unduly shunting electric current through the upper part of the charge. A low and deeply-buried electric smelting zone is necessary to enable the heat to be retained by the charge, and to prevent excessive atmospheric oxidation of the carbon electrodes where exposed. Nevertheless, the reaction-gases must find ready exit through the charge-body along lines nonadjacent to the electrodes, necessitating a charge of high and uniform porosity. The charge-materials now employed to meet these requirements must be carefully selected, and are expensive.

According to the present invention, a

charge having the desired'characteristics is provided by the use of cheap materials. The iron element may be either scrap-iron or iron oxid, for example mill-scale. The silicon element is preferably ground silica sand, or finely-crushed quartz. The carbon element may be any cheap form of coal or coke, for example coking bituminous coal, or cokeoven waste or fines. The amount of carbon should be slightly in excess of that theoretically requisite for reduction of the silica, the silica and carbon formed into briquets or agglomerates, of definite or'indefinite shape and size. If coking coal is used, no binder may be necessary, and the agglomerates are coked to eliminate the volatile hydrocarbons, which may be collected and burned to supply heat. for coking. If

coke is used as the carbon element, a binder of sodium silicate or sulfite pitch is suitable.

While it isnecessary that the furnace-charge as awhole should be highly porous, it is also important that the individual agglomerates should be strong, infusible and impermeable, to prevent their premature crushing, softening and disintegration in the furnace, under the Weight of the charge, and the heating and oxidizing effect of the escaping gases, before they reach the silicon-reduction zone.

A charge-body of such hard, impermeableagglomerates, containing both the ore and reducing agent, is highly and uniformly porous, and has a low electrical conductivity. Such charge may be of considerable depth and yet may be smelted by the use of electrodes extending down through it nearly to the hearth of the furnace, keeping the silicon-reduction zone low and efiectively retalnlng the heat, except that carried off by the efliuent gases, which is usefully absorbedby the upper portions of the descending charge.

According .to the preferred process, the charge is smelted in a combined combustion and electric furnace, in which there are three separate and distinct zones of reaction: a preliminary preheating zone, an intermediate iron-reduction zone, and a final electric silicon-reduction zone. The carbon monoxid generated by the electric smelting of the briquets of silica and carbon, in the presence of the reduced iron, is passed through the incoming preheated charge,v

thereby immersing the briquets in a reducing atmosphere, and-serving to protect exposed carbon of the briquets against oxidation in its'travel through the furnace, at the same time effecting the iron-reduction, and

.the residual carbon monoxid is then burned with injected air to effect the preheating, the final reacti0n-gases escaping from the furnace at a relatively low temperature andv downward through the same into the electric walls 2 and an arched roof 3 having a central opening 4:. Electrodes 5, in the furnace illustrated twelve in number, extend downward through openings 6 in the roof into the smelting chamber, these electrodes preferably converging somewhat toward their lower ends. Each of these electrodes enters through a water-cooled gas-tight stuffingbox 7, and may consist of several rods of graphite, secured to each other end to end. Each electrode is carried by an adjustable holder 8 and is connected to the source of current by a main 9. These electrodes are preferably connected to the terminals of a multiphase generator, the hearth of the furnace being either neutral or connected to the generator, for example to the common point of a delta-wound generator. The roof 3 has manholes 10 with gas-tight closures 11. Supported directly above the roof-opening 4 is a stack combustion-chamber 12, the lower end of which is connected to the roof of the electric furnace by a sand-sealed gas-tight joint 13. Radial twyers 14: connected to a bustle-pipe 15 open through the lower end of the stack. The stack may be cooled by a water spray delivered onto its outer surface by an annular perforated pipe 16, the excess water flowing downward over the roof of the electric furnace. In practice, the charge for this furnace may consist of mill-scale, Fe O intermingled with dense impermeable briquets of ground sand and coke, the carbon being slightly in excess of that requisite for the reduction of the silica. The theoretical charge for the production of. fifty-per cent. ferrosilicon is indicated by th'eequation- Assuming that 95 per cent. of the iron and 90 per cent. of the silicon are reduced from their oxide. and that the excess carbon is insufiicient to reduce the iron oxid, 226 kilograms of this ferrosilicon requires for its production about 169 kilograms of millscale, 269 kilograms of sand and 139 kilograms of coke containing 80 per cent. of carbon. This charge is fed into the top of the stack 12, and during the smelting gravitates furnace. The preheating of the charge is effected in that portion of the column above the twyers 11, by the combustion of the carbon monoxid rising from below. The temperature of the charge arriving at the twyers may be about 1,532 C. The preheated charge passes into the intermediate zone, extending downward from the twyers to or into the electric furnace, in which zone the reduction of the iron is efiected by the carbon monoxid evolved by the silicon-reduction, and the reduced iron and briquets,

raised by the reaction in this intermediate zone to a temperature of say 2,000 0., pass on into the final zone wherein the reduction of the silica is electrically effected, the temperature in this zone also being say 2,000 C. and the consumption of electric current being simply that required to effect the reduction and offset heat-losses. The reaction in the bottom zone may be represented by the equation The reaction in the middle zone may be represented by the equation- The reaction in the top zone may be represented by the equation As indicated by these equations, threeeights of the carbon monoxid. evolved by the silicon-reduction is sufficient to effect the iron-reduction, the remaining five-eighths being available for preheating the charge. The twyers are so located that air is introduced at the proper point to effect this combustion and raise the charge to a suitable temperature for the iron-reduction, while allowing a temperature-gradient upward to the top of the furnace such that the efliuent gases have a comparatively low temperature and. contain little carbon monoxid. The. air introduced through the twyers quietly burns the carbon monoxid, which is at a high tem" perature and is initially diluted with threefifths its volume of carbon lioxid. Little oxidation of the carbon in the briquets results, since but little carbon is exposed to the action of the air by reason of the impermeability of the briquets, and since the air preferentially tends to combine with the carbon monoxid. Furthermore, freeoxygen disappears from the gases at a point not far above the twyers, so that no oxidation of carbon can occur in the upper part of the charge except by reduction of the carbondioxid in the gases, this reaction being minimized by the comparatively low temperature of the charge in the major part of the preheating zone.

The process is preferably operated continuously, ferrosilicon being tapped from the electric furnace and fresh charge-mixture being supplied to the top of the stack furnace, as required.

I claim:

1. The process of producing ferrosilicon, which consists in electrically smelting agglomerates containing silica with carbon slightly in excess of that required to reduce the silica, in presence of iron.

2. The process of producing ferrosilicon, which consists in electrically smelting a porous charge-body consisting of hard, impermeable agglomerates containing silica with carbon slightly in excess of that required to reduce the silica, in presence of iron.

3. The process of producing ferrosilicon, which consists in feeding a charge containing agglomerates of silica with carbon slightly in excess of that required to reduce the silica and a source of iron through a preheating zone into a zone wherein siliconreduction and alloying is electrically effected, with evolution of carbon monoxid, and utilizing said carbon monoxid to effec the preheating.

the iron and agglomerates into a final zone wherein silicon-reduction is electrically effected, with production of carbon monoxid, and utilizing said carbon monoxid to eflect the iron-reduction.

5. The process of producing ferrosilicon, which consists in feeding a charge comprising agglomerates of silica with carbon slightly in excess of that required to reduce the silica andan iron compound through a preheating zone into an intermediate zone wherein iron-reduction is effected, delivering the iron and agglomerates into a final zone wherein silicon-reduction is electrically effected, with production of carbon monoxid, utilizing a portion of said carbon'monoxid to effect the iron-reduction, and burning the residual carbon monoxid to effect the preheating.

6. The process of producing ferrosilicon, which consists in gradually moving a chargecolumn initially. consisting of dense impermeable agglomerates of silicon with carbon slightly in excess of that required to reduce the silica and a pulverulent iron compound downward through a combustion-chamber into an electric furnace, preheating the charge at the upper portion of said column, reducing the iron compound within the lower portion of said column, reducing the silica in the presence of the reduced iron within said electric furnace, and passing the gaseous reaction-products from said electric furnace into said combustion-chamber and therein utilizing them to effect the ironreduction and charge-preheating.

7. The process of producing ferrosilicon, which consists in gradually moving a chargecolumn initially consisting of dense impermeable agglomerates of silica with carbon slightly in excess of that required to reduce the silica and a pulverulent iron compound downward through a combustion-chamber into an electric furnace, preheating the charge at the upper portion of said column, reducing the iron compound within'the lower portion of said column,reducing the silica in the presence of the reduced iron within said electric furnace, and passing the gaseous reaction-products from said electric furnace into said'combustio'n-chamber and thereinutilizing them to effect the iron-reduction and' finally burning them with air to effect the preheating. v

8. The process of producing ferrosilicon, which comprises electrically smelting a selfcombustible mass containing carbon and silica in the presence of iron, said carbon being protected from external oxidation by said silica.

9. The process of producing ferrosilicon, which comprises electrically smelting a selfcombustible mass containing carbon and silica in the presence of iron, said carbon being protected from external oxidation by said silica and evolving carbon-monoxid upon smelting, and preheating said self-coming the iron and agglomerates into a final zone wherein silicon-reduction 'is electrically effected with production ofcarbon monoxid, retarding the oxidation of carbon 'in the agglomerate in its downward passage by the 1 

